1. Field of the Invention
The present invention relates to locomotive air supply systems and, more particularly, to an air supply control system for optimizing operation of the air supply system when a locomotive is about to enter into a tunnel.
2. Description of the Related Art
Heavy haul freight trains such as those operated in North America typically have four to seven 4500 horse power diesel locomotives in a consist at the head end of the train to provide the required tractive effort. The first locomotive in the consist is typically called the lead locomotive and the remaining locomotives in the consist are generally referred to as the trailing locomotives. The tractive effort (propulsion) and brakes on the trailing locomotives are controlled by the driver in the lead locomotive.
When the locomotive consist travels through a tunnel, the multiple high-horse power locomotives can produce ambient temperatures in the tunnel as high as 140° C. (284° F.) at the location of the trailing locomotives. This very high ambient temperature is the result of both the accumulated waste heat from the locomotives and inefficient combustion at the trailing locomotives due to the oxygen depletion that results from the operation of the lead locomotive.
Traditionally, the air compressors on the locomotives are operated based on local pressure governor controls. The air compressors are turned on when the pressure in the first main reservoir drops to about 120 psi and turned off when the pressure in first main reservoir increases to 140 psi. Desiccant-type air dryers used to dry the compressed air produced by the air compressors regenerate the material in the desiccant bed by purging the desiccant bed with dry air from the main reservoir system on an independent cycle as determined by the air dryer or on an independent cycle determined by the air dryer only when the compressor is operating.
A typical two-stage locomotive compressor generally includes a first pressurization stage, an intercooler, a second pressurization stage, and an aftercooler. The internal air temperature in the second stage may be as high as 300° F. above ambient temperature due to the heat of compression. This air is cooled to 20° F. to 40° F. above ambient by the aftercooler before it is supplied to the main reservoir system.
In a tunnel, where the ambient temperature can reach 140° C. (284° F.) at the trailing locomotives, the internal temperature in the second stage of the air compressor can reach up to 600° F. due to the high initial ambient temperature and the heat of compression. Operating temperatures in this range can result in high rates of wear and degradation of the air compressor. Furthermore, the outlet temperature of 324° F. resulting from the high ambient temperature plus the 20 to 40° F. cooling delta of the aftercooler can degrade the air dryer as its treats the overly hot air discharged from the compressor. Thus, there is a need in the art to protect the air supply system from the overly hot air in a tunnel.